100 NEW ZEALAND NATURE-STUDY BOOK 
of pores, and with the large inner cavity or cavities by a 
system of canals. The water containing a food supply 
with the dissolved oxygen which the animal requires, 
enters through the pores, flows into the chambers along 
the passages, and through the central cavity from which it 
is finally discharged. The flow of the water through these 
passages is brought about by the whip-like ciliae which 
grow from the walls of the chambers, and are continually 
lashing the water and so driving it forward. As the water 
moves along the passages which ramify in all directions, the 
animal is able to absorb the nutritious matter it contains, 
as well as obtain a supply of dissolved oxygen. The 
sponge is continually in need of nourishment, hence the 
necessity of the constant flow of water through the 
channels, and hence therefore, the importance, indeed actual 
need, of the incessant movement of the ciliae. It will be 
noticed that the pores through which the water enters are 
much smaller than the canals along which it subsequently 
flows, an arrangement which prevents the blocking up or 
choking of these minute external openings. 
When the sponge is first obtained, it is covered with a 
soft living jelly very like the white of an egg. ‘This is the 
flesh which is supported on that part of the animal which 
we call the skeleton. The common sponge so constantly in 
use in our homes may therefore be described as the skeleton 
of a marine animal. Part of the jelly drains away as soon 
as the animal is removed from the water; the rest is got 
rid of by squeezing and wringing, by stamping underfoot, 
or by pounding with wooden mallets. After this the 
sponges are thoroughly dried in the air, and further 
cleaned and bleached ; they are then ready for the market, 
The common sponge grows in warm seas—great quantities 
being obtained from the Mediterranean and considerable 
numbers round the Australian coasts. It is found attached 
